1. Field of the Invention
The invention relates to a bleach catalyst, processes for its preparation and bleaching compositions incorporating this catalyst.
2. The Prior Art
Dry bleaching powders, such as those for cleaning laundry, generally contain inorganic persalts as the active component. These persalts serve as a source of hydrogen peroxide.
Normally, persalt bleach activity in aqueous solution is undetectable where temperatures are less than 100.degree. F. and delivery dosages less than 100 ppm active oxygen. The art has recognized, however, that bleaching under mild conditions may be effectuated through the use of activators.
U.S. Pat. No. 3,156,654 discloses heavy metal ions such as cobalt in combination with chelating agents to catalyze peroxide decomposition. U.S. Pat. No. 3,532,634 suggests a similar approach but with cations that are transition metals having atomic number 24 to 29. Neither system is totally satisfactory.
Bare metal ions, even when chelated, accelerate wasteful decomposition reactions that are non-bleach effective. Under alkaline conditions, as with laundry cleaning compositions, metal ions undergo irreversible oxidation. Perversely, the peroxide bleaching reaction is most effective at high pH. Furthermore, the prior art metal ion catalysts are sensitive to water hardness. Their activity varies with the calcium and magnesium content of the water source.
Manganese (II) salts have been reported to be exceptionally effective in activating persalts under mild conditions. European patent application No. 0 082 563 discloses bleach compositions containing manganese (II) in conjunction with carbonate compounds. British patent application No. 82 36,005 describes manganese (II) in conjunction with a condensed phosphate/orthophosphate and an aluminosilicate, the builder combination enhancing bleach performance.
The aforementioned compositions stil suffer from the presence of soluble manganese (II) ions. When utilized for whitening laundry, the soluble ions deposit on fabrics. Strong oxidants, such as hypochlorites, are frequently included in laundry washes. Deposited manganese will react with strong oxidants to form highly staining manganese dioxide.
European patent application No. 0 025 608 reveals to peroxide decomposition catalyst consisting of zeolites or silicates whose cations have been exchanged for heavy metals such as manganese. Co-pending U.S. application Ser. No. 597,971, now U.S. Pat. No. 4,536,183 discloses a bleach activator comprising a water-soluble manganese (II) salt adsorbed onto a solid inorganic silicon support material, the combination having been prepared at a pH from 7.0 to 11.1. Although these systems provide adequate bleaching, more potent catalysts would be desirable where the amount of catalyst must be kept at a low level. Economics, peroxide stability, compatibility and environmental considerations encourage use of activator systems with the highest possibe activity.
U.S. Pat. No. 4,208,295 (Sai et al.) discloses bleaching detergent compositions wherein water-insoluble aluminosilicates have had their cations partially exchanged with calcium or magnesium ions. Incorporation of calcium and magnesium was found to improve the storage stability of sodium percarbonate. Evidently, these particular divalent cations were not considered as bleach accelerators but, rather, as stabilizers to prevent decomposition of peroxide.
Consequently, it is an object of the present invention to provide a bleaching composition containing a persalt and a manganese bleach catalyst that will not result in substrate staining.
A further object of this invention is to provide a nonstaining bleach composition exhibiting exceptionally high bleach performance.
Another object of this invention is to provide a process for the preparation of manganese bleach catalysts.